Domantas Sabonis, the forward caught by surprise when the Oklahoma City Thunder traded him to the Indiana Pacers last July, was in store for even more shock when he arrived in Indianapolis for summer workouts: Bill Bayno, an assistant coach for the Pacers, outfitted himself with huge pads on his arms, which he wielded like clubs as Sabonis drove to the basket.

“Just wanted to teach him how to use his body,” Bayno said after a recent practice, adding: “He’s picked that up really quick.”

That assessment could apply to countless elements of Sabonis’s first season with the Pacers, a team that, in a span of mere months, went from presumed Eastern Conference doormat to N.B.A. playoff contender, with a first-round series against the Cleveland Cavaliers.

For the Pacers, who play Game 1 in Cleveland on Sunday, so much about their surprising season — and they were, by far, the biggest surprise in the league this season — hinged on Sabonis, a 21-year-old former star at Gonzaga, and another newcomer, Victor Oladipo, 25, who helped spur the team to a 48-34 record and the fifth seed in the East.

Nobody is taking the Pacers lightly anymore.

“I feel like certain people have waited for them to come down all season, but they’re not coming down,” J. J. Redick of the Philadelphia 76ers said. “They’re a great basketball team.”

Oladipo and Sabonis have provided the Pacers with more punch than anyone could have reasonably projected. During the regular season, Oladipo — liberated from the various challenges of playing alongside Russell Westbrook in Oklahoma City — averaged career highs in points (23.1), rebounds (5.2), assists (4.3) and steals (2.4), and was named to his first All-Star team.

“It goes to show you the importance of being in the right situation, of playing for a coach that puts you in good positions,” Redick said, referring to the Pacers’ Nate McMillan. “For 80 to 90 percent of the league, that’s what it’s all about.”

Sabonis made a seismic jump in his own development, averaging 11.6 points and 7.7 rebounds while shooting 51.4 percent from the field, mostly off the bench.

“He’s been everything we thought he would be and more,” Bayno said.

There is a unique kinship between Oladipo and Sabonis, who have been traded together — twice. Sabonis’s rights were included in a draft-night trade in 2016 that sent him and Oladipo, along with Ersan Ilyasova, from the Orlando Magic to the Thunder.

“It’s just a special bond, man,” Oladipo said. “He’s like my little big brother. I can talk to him about anything, and he can talk to me about anything.”

The Pacers acquired them last summer when Paul George, a five-time All-Star who had spent his entire career with the team, made it clear that he wanted out of Indiana. Given George’s trade demand, the Pacers did not have a ton of leverage. They eventually struck a deal with the Thunder, who agreed to trade Oladipo and Sabonis for George. No player was more synonymous with the franchise. Now, he was gone.

At the time, words like “fleeced” and “pathetic” were used in various reports to describe the transaction. In fairness, neither Oladipo nor Sabonis seemed capable of coming close to filling the void left by George.

Oladipo, in his lone season with the Thunder, averaged 15.9 points and 2.6 assists a game toiling in Westbrook’s shadow. And Sabonis, as a first-year player, averaged 5.9 points a game while shooting 39.9 percent from the field.

This was the grand haul the Pacers collected for George? It was almost incomprehensible.

“Everybody thought we were going to be a lottery team,” Bayno said.

Yet Bayno said he had no doubt that last summer’s trade affected both players.

“I think it motivated Vic and Domantas,” Bayno said, “because they both have supreme confidence in their abilities.”

Not long after he was traded, Sabonis, who is from Lithuania, took himself off the roster for the country’s appearance at the FIBA EuroBasket tournament so he could move to Indianapolis and start working with the coaching staff several weeks ahead of training camp.

It was not an easy decision. The head of the Lithuanian basketball federation happens to be his father, Arvydas Sabonis, the Hall of Fame center.

“To miss that really hurt,” Domantas Sabonis said. “It’s a big deal for the country. It means more than anything.”

But Sabonis and the Pacers clearly benefited from his early arrival. Sabonis found Bayno waiting for him at the team’s practice facility with those pads, which he used to batter Sabonis on drives to the basket. Bayno was trying to teach Sabonis to use his shoulder to initiate contact and knock his defenders off-balance.

By December, Bayno was challenging Sabonis to become “the best passing big man” in the league. Bayno could sense that Sabonis had rare vision and touch for a player his size. More growth is ahead.

“We’re working on finding that balance between shooting when he’s open and kicking it out when he draws a crowd,” Bayno said. “Because there are times where he’ll attack and have three guys on him, and that’s the only time when he has a tough time making those decisions.”

Sabonis does not shy away from physical play. Before a recent game against the 76ers, he wore a gash on his face — an artifact of one such collision. Then, during the game itself, he went out and sprained his left ankle.

Sabonis has since returned, showing more polish than ever. Against the Charlotte Hornets on April 8, he scored a career-high 30 points and grabbed eight rebounds.

“I’m still learning,” Sabonis said. “I’m not even close. I experience new things every game.”

With a playoff matchup looming against LeBron James and the Cavaliers, Sabonis is about to experience even more.

Email Scott Cacciola at Scott.Cacciola@nytimes.com and follow him on Twitter:@ScottCacciola.